Fair Value Measurements (Reconciliation of Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value measurement, transfers between activity levels	$ 0	$ 0
Derivatives (net)
Balance at beginning of period	(113,000,000)	(114,000,000)
Purchases, sales, issuances and settlements:
Settlements	(12,000,000)	(14,000,000)
Total gains included on the Condensed Consolidated Balance Sheet	10,000,000	4,000,000
Balance at end of period	(115,000,000)	(124,000,000)
Duke Energy Indiana [Member]
Derivatives (net)
Balance at beginning of period	22,000,000	27,000,000
Purchases, sales, issuances and settlements:
Settlements	(10,000,000)	(14,000,000)
Total gains included on the Condensed Consolidated Balance Sheet	(7,000,000)	(6,000,000)
Balance at end of period	5,000,000	7,000,000
Piedmont Natural Gas [Member]
Derivatives (net)
Balance at beginning of period	(141,000,000)	(142,000,000)
Purchases, sales, issuances and settlements:
Total gains and settlements	20,000,000	10,000,000
Balance at end of period	$ (121,000,000)	$ (132,000,000)